Method and apparatus for indicating repetition intervals of a specified component of a composite electrical signal, particularly useful for displaying fetal r-waves

Abstract

The method and apparatus particularly are applicable for displaying the fetal R-wave with respect to the maternal R-wave, and comprise the steps of generating a first electrical signal corresponding to the second derivative of the composite signal (maternal R-wave); generating a second electrical signal corresponding to the second derivative of the composite signal after the specified component has been removed; subtracting the second electrical signal from the first electrical signal to produce a third electrical signal; and utilizing the third electrical signal for indicating the repetition intervals (fetal R-waves) of the specified component.

What is claimed is: 
     
       1. A method of indicating the repetition intervals of a specified component of a composite cyclically-repeating electrical signal, comprising the steps: generating a first electrical signal corresponding to the second derivative of said composite signal;   generating a second electrical signal corresponding to the second derivative of said composite signal after said specified component has been removed;   subtracting said second electrical signal from said first electrical signal to produce a third electrical signal;   and utilizing said third electrical signal for indicating the repetition intervals of said specified component.   
     
     
       2. The method according to claim 1, wherein said second electrical signal is subtracted from said first electrical signal by first preparing a template representing an average of a plurality of cycles of the second electrical signal, and subtracting said template from the first electrical signal. 
     
     
       3. The method according to claim 1, wherein said third electrical signal is utilized for indicating the repetition intervals of said specified component by: generating a fourth electrical signal corresponding to the first derivative of said composite signal, generating a fifth electrical signal corresponding to the first derivative of said composite signal after said specified component has been removed, subtracting said fifth electrical signal from said fourth electrical signal to produce a sixth electrical signal, adding said sixth electrical signal to said third electrical signal to produce a seventh electrical signal, and integrating said seventh electrical signal. 
     
     
       4. The method according to claim 3, wherein said fifth electrical signal is subtracted from said fourth electrical signal by first preparing a second template representing an average of a plurality of cycles of the fifth electrical signal, and subtracting said second template from said fourth electrical signal. 
     
     
       5. The method according to claim 1, including the further step of displaying the repetition intervals of said specified component. 
     
     
       6. The method according to claim 5, including the further step of displaying the composite electrical signal with the repetition intervals of said specified component superimposed thereover. 
     
     
       7. The method according to claim 1, including the further step of recording the repetition intervals of said specified component. 
     
     
       8. The method according to claim 7, including the further step of recording the composite electrical signal with the repetition intervals of said specified component superimposed thereover. 
     
     
       9. The method according to claim 1, wherein said composite electrical signal is an abdominal ECG signal of a pregnant woman including both the maternal R-wave and the fetal R-wave, and said specified component of the composite signal is the fetal R-wave. 
     
     
       10. Apparatus for indicating the repetition intervals of a specified component of a composite cyclically-repeating electrical signal, comprising: means for generating a first electrical signal corresponding to the second derivative of said composite signal;   means for generating a second electrical signal corresponding to the second derivative of said composite signal after said specified component has been removed;   means for subtracting said second electrical signal from said first electrical signal to produce a third electrical signal;   and means for utilizing said third electrical signal for indicating the repetition intervals of said specified component.   
     
     
       11. The apparatus according to claim 10, wherein said means for subtracting said second electrical signal from said first electrical signal comprises means for first preparing a template representing an average of a plurality of cycles of the second electrical signal, and means for subtracting said template from the first electrical signal. 
     
     
       12. The apparatus according to claim 10, wherein said means utilizing said third electrical signal for indicating the repetition intervals of said specified component comprises: means for generating a fourth electrical signal corresponding to the first derivative of said composite signal, means for generating a fifth electrical signal corresponding to the first derivative of said composite signal after said specified component has been removed, means for subtracting said fifth electrical signal from said fourth electrical signal to produce a sixth electrical signal, means for adding said sixth electrical signal to said third electrical signal to produce a seventh electrical signal, and means for integrating said seventh electrical signal. 
     
     
       13. The apparatus according to claim 12, wherein said means for subtracting said fifth electrical signal from said fourth electrical signal comprises means for first preparing a second template representing an average of a plurality of cycles of the fifth electrical signal, and means for subtracting said second template from said fourth electrical signal. 
     
     
       14. The apparatus according to claim 13, wherein said means for preparing said two templates comprises a threshold detector to preset the threshold level for the templates. 
     
     
       15. The apparatus according to claim 13, further including amplitute control means for amplitude matching said two templates to said first and fourth electrical signals, respectively; and delay control means for time matching said two templates to said first and fourth electrical signals, respectively. 
     
     
       16. The apparatus according to claim 15, wherein said composite signal is an abdominal ECG signal of a pregnant woman including both the maternal R-wave and the fetal R-wave, and said specified component of the composite is the fetal R-wave; said apparatus further including electrode means for detecting said abdominal ECG signal used for generating said composite signal. 
     
     
       17. The apparatus according to claim 16, wherein said apparatus further includes a first filter receiving said abdominal EGC signal and having a cut-off frequency between 90-125 Hz to pass a composite signal including both the maternal R-wave and the fetal R-wave, which composite signal is used for generating said first and fourth electrical signals; and a second filter, constituting said means for removing the fetal signal, receiving said abdominal ECG signal and having a cut-off frequency between 20-30 Hz to pass substantially only the maternal R-wave, which is used for generating said second and fifth electrical signals. 
     
     
       18. The apparatus according to claim 17, further including display means for displaying the repetition interval of the fetal R-wave superimposed over the maternal R-wave, and recording means for recording the repetition interval of the fetal R-wave superimposed over the maternal R-wave. 
     
     
       19. The apparatus according to claim 10, wherein the apparatus includes discrete circuits for performing the defined operations. 
     
     
       20. The apparatus according to claim 10, wherein the apparatus includes a microprocessor programmed to perform the defined operations.